Thermal cut-out



Patented' Nov. 27, 1928.

UNITED STATES PATENT OFFICE.

MAURITS J'. SANDIN, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMRANY, A CORPORATION OF PENNSYL- 'VANIA.

'Tiananmen CUT-OUT.

.Application letl January 23, 1923. Serial No. 614,381.

' My invention relates to thermal cutouts and particularly to cutouts of the screw-plug 'type for interrupting circuits under overload and short-circuit conditions.

In my co-pending application Serial Nb. 614,379, tiled January 23, 1923, I have disclosed a cutout of the plug type wherein an insulating receptacle is provided with a threaded terminal that'is adapted to beinserted in a standard fuse screw socket or receptacle. A thermal-responsive cutout refill connectsthe terminals of the cutout and is adapted to cause interruption of the circuit under overload and short-circuit conditions. The cutout described in the above copending application is adapted for operation in circuits having a capacity approximately above five amperes, depending upon the size of the heating conductor of the thermal-responsive rell. y,

It is an object of my invention to provide a thermal cutout similar in general characteristics to the device shown in the above copending application, but which is adapted for use in circuits operating on smaller currents such as from a fraction of an ampere to ive amperes/or the minimum range of the cutout device referred to above.

It has been found that the heat-conducting characteristics of adevice constructed in accordance with the disclosure inthe above copending application are such that, in order to cause suflicient heating to interrupt the circuit under small current conditions, such, for instance, as a current of one ampere, the crosssectional area of the heating conductor required would be so small that the 'refill would V be impractical for commercial purposes.

Another object of my inventlon is to pro.-

vide a thermal-responsive cutout having such heating characteristics that a heating conductor of practicable dimensions maybe employed which will cause the interruption of the circuit on relatively low-current conditions.-

iAnother object of'my invention is to provide a thermal-responsive cutout device, having the above characteristics, wherein the refill is of simple and rugged construction suitable or commercial use and wherein the re- -fill isiof such character `that it may be used in a cutout casing such as may be used for rei.

ills having greater capacity. l These and other objects, that will be made apparent throughoutthe further description of my invention, are attained by means of the apparatus hereinafter described, and illustrated in the accompanying drawings, wherein:

Figure 1 is a vertical section through a cutout embodying my invention; l

Fig. 2 is a transverse section through the cutout device taken on the line lI-II of l Fiv. 1, and

Fig. 3 is a vertical Sectio through a cutout device, showing a modi ed form of thermal-responsive refill. y Referring tothe drawings, the cutout devifce includes an insulating casing or tubular receptacle 4 closed at one end and having bores 5 and 6 extending longitudinally thereof, the latter being of greater diameter than the former. A tubular terminal member 7 is mounted Vin the closed end of the receptacle or casing 4 and is retained therein by a ange 8 that is spun into contact with the inner surface of the end Wall of the casing.

A threaded terminal 9 is mounted on the outer surface of the casing 4\which is adapted to fit within a standard threaded socket or receptacle (not shown). A terminal dise 11 is mounted within the bore 6 of the casing and is provided with a perforation 12 through which the heating conductor of a thermalresponsive refill 13 is inserted, the refill serving to connect the terminal 11 with the tubular terminal 7. The refill comprises a contact disc 14 to which a heating conductor 15 made of high-resistance metal is attached by means of an enlarged head 16 on the conduc- 9o tor 15, which is secured to the Contact disc 14g by means of F:solder or by any preferred means.'

A heating conductor 17, similar to the bonductor 15, is releasably connected to the free end of the conductor 15 by a readily fusible metal that is soldered to the adjacent ends of the conductors and ametal container 18 that is of U-shape, as indicated in Fig. 2, and which serves to support the solder during the assembly operation of the parts constituting 100 the rell. The heating conductor 17 is adapted to extend into a bore 19 in the terminal 7, as indicated in Fig. 1, and is clamped therein by means of a set screw 21. v

The terminal disc 11 is normally biased to- 105 ward the open end of the casing and away from the terminal 7 by means of a helical spring 22 that -is disposed between the closed .end of the casing and the inner end of an inbore 5 of the casing and prevents the escape ot arc gases, incident to the separation of the heating conductors, through the opening 24 in the casing through which a flexible conductor 25, that connects the terminal 9 to the conductor disc 11, extends. An extension 2G, having an inwardly-directed flange 27, serves to limit the outward movement of the disc 11.

The helical spring 22 is protected from are gases by means of an inner insulating tube 28 that is mounted on a spring-supporting disc 29 andwliich is retained in central position by a sleeve 31 that is. attached to the disc 29. An insulating washer 32, that fits within the bore 5 and surrounds the barrier tube 28, serves to seal the joint between the barriers 28 and 23 and protect the spring 22 from are gases, regardless of the relative operative positions of the barrier tubes.

The construction of the casing and the terminal disc 11 and the barriers just described is similar to the construction shown in the above copending application. the only difference being in the form of refill. The open end of the casing is closed by a detachable cap 30 lia-ving a transparent mica window 40 through which it rendeis the refill visible.

In operation, the current flows through the heating conductors 15 and 17. The soldered joint connecting the heating conductors is isolated from the terminal disc 11 and from the terminal tube 7 and, consequently, the joint is located at thehottest point in the heating conductor constituted by the conductors 15 and 17 and Will be substantially unaffected by the heat-radiating characteristics of the terminal disc l1. For this reason, a relatively thick heating conductor may be employed that will cause fusion of the soldered joint under relatively low-current conditions, in fact, the circuit may be interrupted by a device constructed as herein described when subjected to currents of less than one ampere.

If a heating conductor constituting a thermal-responsive refill were soldered directly to the contact .disc 14, as in the manner disclosed in my copending application, the cross-sectional areaV thereof would of necessity be so small, in order' to produce sufiicient heat to overcome the heat-conducting effect of the terminal disc, that the Wire would be impractical and would be of insuiiicient strength to meet the requirements of shipping and handling in commercial use. By providing a heating conductor on both sides of the soldered joint, the cooling effects of heat conduction on the soldered joint are reduced to a minimum and, consequently, less energy is required to cause the interruption` of a circuit and, therefore, the refill operates with greater efficiency'. V Y

In Fig. 3, I have show'n` a cutout mechanism similar to that illustrated in Fig. 1, except that a modified form oi rell is shown, Wherein a relatively rigid supporting wire 33 is soldered to the contact disc 14 and serves to support a relatively tine heating wire 3d that is wound about the supporting wire 33.

Under low-current conditions, the wire 34, which is of relatively great length and insulated from the supporting Wire, causes rapid heating of the supporting wire 33 and subsequent fusion of the binding metal or solder joint which joins the wire to the disc 14. By reason of the supporting wire, a fine heating conductor may be employed and, as indicated, tlie end ot' the heatingl wire is doubled or twisted to constitute a terminal portion 35 that is adapted to be inserted within the bore 19 of the terminal tube 7 where itis retained by a set screw 21.

The retill illustrated iii Fig. 3 is also suitable iior interrupting circuits opera-ting under relatively low-current conditions. lVhen the disc 14 is separated from the supporting wire 33, the spring 22 moves the terminal disc 11 away from the supporting wire and causes interruption of the circuit.

, lVhile l have illustrated and described but two embodiments of my invention it will be apparent to those skilled in the art .that various changes, modifications, substitutions, additions and omissions may be made in the apparatus illustrated Without departing from the spirit and scope of my invention, as set forth in the appended claims l claim as my invention:

l. A cutout for electric circuits comprising a pair of relatively movable terminal members, biasing means tending to move said members apart, a casing for enclosing the terminal members and a composite renewable thermal-responsive element t'or conductively connecting the members and for releasably opposing said biasing means comprising a pair of heating conductors connected respectively to the terminal members and having their free ends releasably soldered to one another by a met-al fusible at a relatively low temperature.

2. In a cutout for electric circuits, the combination with a pair of relatively movable terminal members one`of which is adapted to bebiased for separatingmovement, of a coniposite renewable thermal-responsive element comprising a pair of heating conductors con nected respectively to the terminals and hav- 4ing their f'ree ends releasably connected by a fusible link soldered to the conductors.

'3. A thermal-responsive refill for acircuit'` cutout comprising a pair of heating iconductors joined by a link consisting of a metal supporting member containing fusible metal that is solderedto the supporting member and to the conductorsi 4. A thermal-responsiye reiill for a circuit cutout comprising a pair of heating conductors having'overlapped ends joined by a link consisting of a metal supporting member containing fusible metal that is soldered theadjacent ends of the conductors and con-V to the supporting member and to the conductaining fusible meta'l that is soldered to the tors. c gnductors and to the supporting member. 10

5i A thermal-responsive refill for a. circuit In testimony whereof, I hav'ehereunto sub- 5 cutout comprising a pair of heating conseribed my name "this 9th day of January,

, ductors joined by a link consisting of a metal 1923.

supporting member of U-shape surroundingA A' MAURITS J. .SANDIN 

